Ignition arrangements for internal combustion engines



Oct 14,1969 SQEHNER ETAL I IGNITION ARRANGEMENTS FOR INTERNAL COMBUSTION ENGINES Filed Aug. 22, 1967/ 762 United States Patent Int. Cl. nozk 21/14 US. Cl. 310156 12 Claims ABSTRACT OF THE DISCLOSURE An arrangement for providing ignition pulses to spark plugs of internal combustion engines. A signal generator having a stator and rotor, of saw-tooth cross section, form a magnetic circuit whereby the ignition pulses are generated. The saw-tooth rotor has undercut teeth moving past magnetic poles of the stator. As a result of the motion of the rotor, the fiux density of the magnetic path, linking rotor with stator, is varied between relatively high maximum or minimum values. This variation in the magnetic flux produces a pulse through inductive effects in the winding situated in the stator. The induced pulse from the stator is transmitted to an electronic circuit which shapes the pulse and provides the spark plugs with a corresponding sharp pulse of the required duration.

Background of the invention The invention includes a signal generator which produces an alternating signal, in an induction coil, having positive and negative portions. For purposes of actuating the electric circuitry, however, only one p0rtion--all of the same polarity, is used from this alternating signal. Thus, only the positive or negative portion of the alternating signal is required. The other portion of the curve with opposite polarity, is undesirable since it may cause destruction of the semiconducting circuitry, when its magnitude becomes too large.

Accordingly, it is essential to provide against such destructive effects in conventional signal generators. In this connection, two methods are essentially known. One method resides in the basis of providing a diode in parallel with the induction coil of the signal generator, so that a short circuit is established for the undesired portion of the alternating signal. This method, however, gives rise to considerable loading effects of the signal generator and produces armature feedback effects resulting in a lag of the ignition instant for high rotational velocities. In the other method, a diode is connected in series with the induction coil, in order to permit passage of only that portion of the alternating signal, which is of the desired polarity. This method has the disadvantage that for low rotational velocities, the voltage drop across the diode becomes significantly undesirable. Reliable operation of the ignition arrangement is essential for low rotational velocities, in order to assure starting of the engine. The rotational velocity, when starting, can be especially small when the battery is insufiiciently charged or the temperature is relatively low. The signal generator is relied upon, however, to provide sufiiciently large voltage signals for ignition purposes, even under these conditions. This requirement becomes difficult to fulfill, however, when the diode is series connected.

One of the objects of the present invention, is to avoid the disadvantages of the conventional signal generators for ignition arrangements. In particular, it is an object of the present invention to provide a signal generator which produces minimum lag in the ignition instant,

3,473,061 Patented Oct. 14, 1969 when applied to the advantages arrangements without mechanical contacts. At the same time, it is also an object of the present invention to provide a sufiiciently large ignition voltage at low starting speeds. A further object of the present invention is to provide a design for the signal generator, whereby the latter may be simply and economically constructed.

The invention achieves these objects through a signal generator having a rotor which has a saw-tooth cross sectional area. The saw-tooth design of the rotor provides for steeply inclined edges as well as gradually sloping edges or surfaces. The signal generator is designed with the special advantage that the base of the saw-tooth exceeds one half the distance between adjacent peaks of the saw-teeth. The voltage signal produced by the gradually sloping surface of the saw-tooth, is of relatvely small magnitude since the rate of variation of the flux is relatively low. In this manner it is possible to avoid the safety devices, described supra, for protecting the semiconducting circuitry. It is thus apparent that the gradually sloping edge or surface is of special constructional significance. For example, if the rotor were to possess numerous or many teeth, the back of any one tooth could extend only over a relatively small amount of space between two adjacent teeth. If on the other hand, only a small number of saw-teeth are applied, the back of any one tooth may extend over a larger amount of space. The radius of the generator, generally built into the distributor, is here also of significance.

The signal generator is further constructed, in an advantageous manner, so that a recess prevails between the undercut edge of a tooth and the back end of the adjacent tooth. This undercutting of the saw-tooth is especially advantageous because it provides for a particularly large portion of the voltage used for ignition purposes.

In designing the saw-tooth, and the rotor, it is desirable that the gradually sloping surface have the shape whereby the magnetic flux may increase linearly with the rotation of the rotor. In generators having radial teeth, the gradually sloping edge or surface is designed so that its cross section is in the form of an Archimedian spiral. In this manner the portion of the alternating signal, which is not used, remains at a relatively low value and is constant with the angular rotation.

Summary of the invention The main object of the present invention is to provide specifically shaped and sharp pulses to spark plugs in an internal combustion engine. These ignition pulses are produced through a signal generator having stator and rotor members. An induction coil is mounted on the stator and has terminals leading to the exterior thereof. The rotor member rotates within the stator and is magnetically linked with the field produced by the stator. The rotor member has a plurality of saw teeth each shaped to include a steeply inclined edge connecting with a gradually sloping edge terminating in a recess. As a result of this construction of the rotor and stator, the magnetic flux linking the stator and rotor members is varied periodically as the rotor member rotates with respect to the stator. The output of this signal generator are thus pulses of the required magnitude and duration. An electronic circuit connected to the output of the signal generator serves to shape the pulses so that they are of the required characteristics for igniting the spark plugs.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

Brief description of the drawing FIG. 1 is a longitudinal cross sectional view of a signal generator, in accordance with the present invention, when applied to a four cylinder four cycle internal combustion engine;

FIG. 2 is an end view of the signal generator taken along lines II-II in FIG. 1;

FIG. 3 is a graphical plot of voltage as a function of the rotational angle of the signal generator; and

FIG. 4 is an electrical schematic diagram of the switching circuitry applicable to the signal generator.

Description of the preferred embodiments Referring to the drawing, and in particular FIG. 1, the signal generator comprises essentially a stationary part or stator 10, and a movable part or rotor 11. The stator and rotor are linked by a magnetic circuit. As shown in FIG. 2, the stationary part has a cylindrical exterior surface 12. The stator 10 is also provided with a bore 13 to permit a driving shaft 14 to pass therethrough. The bore 13 forms the wall of a concentric portion about the shaft 14, which forms a recess 15. The recess 15 serves to retain an excitation coil 16 and an induction coil 17. The terminals 18, 19, 20, and 21, of these two coils, are led to the exterior of the generator. The stationary part 10 terminates in four poles 24, of rectangular cross section, displaced from one another by 90 degrees.

A hollow cylindrical part 25 is secured to the driving shaft 14. The outer diameter of the cylindrical part 25 is only somewhat smaller than the inner diameter of the bore 13 within which the part 25 extends. The part 25 terminates in a flange 26 adjacent to the end of the wall containing the bore 13. A second hollow cylindrical part 27 consisting of non-magnetic material resides along the longitudinal surface of the shaft 14 and abuts the part 25. A permanent magnet in hollow cylindrical form resides concentrically about the member or sleeve 27. Abutting the north designated end of the permanent magnet 28, is the variable air gap rotor 29. As shown in FIG. 2, the cross section of the rotor is in the form of a circular saw havingfour teeth 30. The back surfaces 33 of these teeth recede toward the rotor center.

The saw teeth 30 at the circumference of the rotor 29, form elevations and recesses. When rotating in the direction shown by the arrow in FIG. 2, the back surfaces 33 present a low incline or rise with respect to the pole 24. The edge 34, on the other hand, presents a very steep rise or incline with respect to the pole 24. The edge 34 is, in fact, in the form of an undercut saw tooth. The construction is such that the rising sufaces 33 extends over more than one half the space between the peaks of successive saw teeth. A recessed surface 36 is interposed and joins the undercut edge 34 with the rising surface 33. The recessed surface 36 has shown itself to be very important in the present invention.

The permanent magnet 28 is polarized in its axial direction, as shown in FIG. 1, through the designations of N and S corresponding to the north and south poles. The permament magnet produces a magnetic path within the magnetic circuit formed by the stator 10 and the rotor 11. FIG. 1 shows a single flux line 35 of this magnetic path. The magnitude of the magnetic flux is dependent upon the orientation of the rotor 11 in relation to the stator. If the rotor is somewhat turned from the position shown in FIG. 2 in the direction shown by the arrows in FIG. 2, the poles 24 will lie opposite the recess surfaces 36. In this position the air gap between the stator and rotor is of a large magnitude and accordingly the magnetic flux is very small in amount. If, now, the rotor is turned further, the poles 24 commence to lie opposite the rising surfaces 33. The rate of rise or incline of the rising surfaces 33 is such that the magnetic flux increases linearly with the angle of rotation. This linear increase is also made quite small so that only a small constant voltage is duced in the induction coil 17. Shortly before the rotor attains the position shown in FIG. 2, the magnetic flux attains a maximum value, and then falls abruply to a low value, due to the undercut edge 34 and the recess surface 36.

The variations in flux induce, within the induction coil 17, an alternating voltage u, shown in FIG. 3. As shown by the graphical plot, this voltage curve is not symmetrical. The portion of the curve lying above the abscissa a or coordinate axis, has an essentially constant instantaneous value u of substantially low magnitude. On the other hand, the portion of the curve lying beneath the abscissa attains a relatively high instantaneous peak 11 This peak is reduced to a value not less than U when operating under load. The dotted curve 14' corresponds to the relationship prevailing when the operation is under load. For purposes of controlling a transistor, it is essential to preserve, or not to drop below, the magnitude U The voltage u is proportional to the angular speed of rotation, not considering the interactions of eddy currents. As a result of a corresponding excitation current within the excitation coil 16, the magnetic flux may be increased or diminished. The magnitude of the voltage can accordingly be varied. Through proper design of the excitation coil, it is also possible to eliminate the necessity for the permanent magnet. Under these conditions, the permanent magnet may be replaced with soft magnetizable material.

FIG. 4 shows an ignition circuit which serves mainly for purposes of clarification. The negative terminal of the battery 40 is connected to ground while the positive terminal is connected to the conducting path 42, by way of an ignition switch 41. The ignition arrangement includes an ignition coil 43 having a primary winding 44 and a secondary winding 45. One end of each of these two windings is connected to ground. The other end of the secondary winding 45 is connected to a slider 46 of a distributor 47. The distributor has four stationary contacts 48 leading to spark plugs 49. The signal generator and distributor disclosed in the preferred embodiment, is adaptable to a four cylinder engine.

The ignition arrangement has, in addition, a monostable multivibrator with two p-n-p transistors 52 and 53, as well as a p-n-p power transistor 54. The base of the transistor 52 is connected to the terminal 21 of the induction coil 17. The other terminal 20, of the induction coil, is connected to the positive conducting path 42. The emitter of the transistor 52 leads to the conducting path 42, by way of a resistor 55. The emitter of the transistor 52 is also connected to the emitter of the transistor 53, through the resistor 56. The emitter of the transistor 53, on the other hand, is connected to the base of the power transistor 54 and to one electrode of the capacitor 57. The other electrode of the capacitor 57 is connected to the conducting path 42.

The collector of the transistor 52 is directly connected to one electrode of the capacitor 58, as well as to ground, by way of the resistor 59. The other electrode of the capacitor 58 is connected to the base of the transistor 53,.directly, as well as to ground, through means of a discharge resistor 62. The latter has a resistance which is large compared with the resistance of the resistor 59. The collector of the transistor 53 is connected to ground, by way of a resistor 63. This collector of the transistor 53 is also connected, by way of the resistor 64, to the base of the transistor 52. The emitter of the power transistor 54 is directly connected to the positive conducting path 42, as well as to the cathode of a Zener diode 65. The anode of this Zener diode is connected to the collector of the power transistor 54. The collector of the transistr 54 also leads to the primary winding 44, by way of the resistor 66.

In the operation, as long as the voltage u in the induction coil 17 is positive, the base of the transistor 52 is positive with respect to its emitter, and the transistor 52 is cut off. Under this condition the transistors 53 and 54 conduct and current flows through the primary winding 44. This current through the primary winding 44 gives rise to a magnetic field. In conjunction with the signal generator according to the invention it is not necessary to provide either a series connected diode 67, or a parallel connected diode 68, with respect tothe coil 17. These two diodes are shown in dotted form, in FIG. 4, and have until now been required in the conventional arrangements. This design has been found to be essential in order to protect the base-emitter path of the transistor 52 from the positive portion of the voltage u. In accordance with the invention, this positive portion never attains a high value, due to the advantageous design provided. As a result severe loading of the signal generator is avoided, as would prevail due to the diode 68. The diode 67, on the other hand, was effective in providing poor starting characteristics.

If, during rotation of the rotor 11, the voltage u becomes negative, the transistor 52 becomes conducting and the transistors 53 and 54 are cut off, when the voltage attains the level U As a result, a high voltage signal is induced in the secondary winding 45 due to the interruption of current in the primary winding 44. This high voltage signal delivered by the secondary winding 45 serves to ignite one of the spark plugs 49.

After a period of time determined by the capacitor 58 and the discharge resistor 62, the transistor 52 is again out olf and the transistors 53 and 54, accordingly, become again conducting. At that time, a new ignition cycle may be commenced. The invention thus provides an improved signal generator for electronic ignition arrangements, through Simple and economic construction.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of ignition arrangements for internal combustion engines differing from the types described above.

While the invention has been illustrated and described as embodied in ignition arrangements for internal combustion engines, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A signal generator for ignition arrangements comprising, in combination, a stator member; an induction coil mounted within said stator and having terminals leading to the exterior of said stator; a rotor member rotatable within said stator and magnetically linked therewith, said rotor member having a plurality of teeth each having a profile formed by a leading edge of spiral curvature and a trailing edge inclined with respect to a diameter of said rotor member passing through the axis of rotation of said rotor member, whereby the magnetic flux linking the stator and rotor members is varied periodically as said rotor member rotates with respect to said stator member.

2. The signal generator as defined in claim 1 wherein said leading edge extends over one half the space between the peaks of two adjacent trailing edges.

3. The signal generator as defined in claim 1 wherein a recess lies between each two adjacent teeth.

4. The signal generator as defined in claim 1 wherein said trailing edge is an undercut saw-tooth.

5. The signal generator as defined in claim 1 wherein the flux linking said stator and rotor members varies linearly through the motion of said leading edge.

6. The signal generator as defined in claim 1 wherein the cross section of said rotor member in form of a circular saw.

7. The signal generator as defined in claim 6 wherein said circular saw cross section has undercut teeth.

8. The signal generator as defined in claim 1 including a permanent magnet within the magnetic circuit linking said rotor and stator members.

9. The signal generator as defined in claim 8 including an excitation coil within said magnetic circuit linking said rotor and stator members.

10. The signal generator as defined in claim 9 wherein said excitation coil is mounted coaxial with said rotor member.

11. The signal generator as defined in claim 1 wherein said induction coil is mounted coaxial with said rotor member.

12. A signal generator for ignition arrangements comprising, in combination, a stator member; an induction coil mounted within said stator and having terminals leading to the exterior of said stator; a rotor member rotatable within said stator and magnetically linked therewith, said rotor member having a plurality of saw-teeth each having, in direction of rotation, a gradually sloping front edge and an undercut steeply inclined rear edge spaced from the gradually sloping front edge of the subsequent saw-tooth by a recess, whereby the magnetic flux linking the stator and rotor members is varied periodically as said rotor member rotates with respect to said stator member.

References Cited UNITED STATES PATENTS 1,587,958 6/1926 Hutton et al. 310- XR 2,446,671 8/1948 Short et a1. l23148 3,322,107 5/1967 Mieras et a1. 123-148 3,356,896 12/1967 Shano 123-148 XR 3,277,870 10/1966 Miki 123-448 XR LAURENCE M. GOODRIDGE, Primary Examiner US. Cl. X.R. 

